The increased use of subsea systems that require large levels of electrical power used to support the functionality of subsea equipment of various types requires the incorporation of large diameter electrical conductors within subsea umbilicals. These conductors invariably dominate the design and manufacturing processes of the umbilical in which they are required and as a result the total fabricated cost of these functional elements invariably dominates the economics of this type of umbilical assembly.
The electrical performance of these types of umbilicals is significantly influenced by the overall operating temperature of the umbilical as this impacts the resistance of these medium voltage conductors and this in turn affects the electrical losses in the cables.
Although these umbilicals are typically many kilometers long, the majority of which operating in a subsea environment surrounded by seawater that keeps the cable operating at relatively cool temperatures, their design is frequently limited by a very short length that is either located in an I-tube located on the side of a floating production storage and offloading vessel (FPSO) or in a large dynamic bend strain reliever (BSR) that is used to protect the power umbilical from being over-bent at the mechanical connection with the FPSO. In cases where the power umbilical is routed through a I-Tube that is located on the side of the FPSO, its operating temperature will be further impacted by the level of solar radiation acting on the external surfaces of the I-tube and the overall ambient temperature.
The design of medium voltage power cable systems are frequently dominated by the operating temperature of a very short section of the overall length of the system leading the use of larger conductors than would otherwise be needed or the use of higher transmission voltages and subsea transformers. In the past, people have used larger, more expensive conductors and/or an expensive transformer.
The various embodiments described herein lower the operating temperature of a short length of an umbilical that previously dominated the system design such that its operating temperature is no longer as much of a factor in the overall system design. In typical designs, the maximum operating temperatures cannot exceed 90° C. One method by which this has been accomplished is to increase the cross-sectional area of the conductors in the umbilical, thereby reducing their electrical resistance. This adds significantly to project costs and in many cases results in additional complications associated with the need to splice conductors during the assembly of the umbilical.